Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 31: Correlated Electrons: Metal Insulator Transition - Part 2

TT 31.3: Talk

Thursday, March 30, 2006, 14:30–14:45, HSZ 301

Raman light-scattering in the Mott-insulators LaTiO₃ and YTiO₃: Evidence for orbital excitations — •C. Ulrich¹, A. Gössling², M. Grüninger³, M. Guennou¹, H. Roth², M. Cwik², T. Lorenz², G. Khaliullin¹, and B. Keimer¹ — ¹Max-Planck-Institut FKF, Stuttgart — ²Universität zu Köln — ³RWTH Universität Aachen

Collective excitations of the valence electrons between different atomic orbitals (termed "orbitons") contain a wealth of information about the different types of interactions between the spin, charge and orbital arrangement of the electrons. Experiments introducing Raman scattering as a direct probe of orbitons in LaMnO₃ [1] have hence opened up new perspectives. However, the results have proven to be quite controversial [2,3]. In order to identify orbital excitations in the titanates LaTiO₃ and YTiO₃ we have used the Raman light scattering technique. The Raman spectrum of these Mott-insulators exhibits pronounced electronic excitations around 230 meV, i.e. well above the energy range of two-phonon excitations. Based on the temperature, polarization, and photon energy dependence, this mode is identified as orbital excitation. The observed profiles bear a striking resemblance to magnetic Raman modes in the insulating parent compounds of the superconducting cuprates, indicating an unanticipated universality of the electronic excitations in transition metal oxides. [1] E. Saitoh et al., Nature 410, 180 (2001). [2] M. Grüninger et al., Nature 418, 39 (2002). [3] E. Saitoh et al., Nature 418, 40 (2002).